Electronic scales can be classified primarily into a load cell type using a strain gauge, a tuning fork vibration type using a tuning fork vibrator and an electromagnetic balancing type using an electromagnet and an electromagnetic coil.
The load cell type makes weight measurements based on the amount of transformation of a strain gauge by a load. As disclosed in a Patent Document 1 hereinafter, the tuning fork vibrator type makes weight measurements by using the fact that the vibration frequency of a tuning fork vibrator is proportional to a load applied between both ends of the tuning fork. On the other hand, the electromagnetic balancing type breaks the balanced condition of a mechanical balance mechanism by a load and recovers the balanced condition by flowing electrical current through the electromagnetic coil, thereby determining the weight of the load based on the amplitude of the electrical current.
As far as precision of these scales is concerned, the tuning fork vibrator type and the electromagnetic balancing type are higher than the load cell type. On the other hand, in the manufacturing cost of these scales, the electromagnetic balancing type is the highest because of its complex construction and the load cell type is the lowest because of its simplest construction.
Currently, most of platform scales having a weighing range (measurement range) up to 300 kg are the load cell type.
However, there are increasing needs in production fields for measuring weight of objects to be weighed in high precision for cases such as, for example, weighing raw bath contained in a drum. This is the reason why it is necessary to improve measurement precision of platform scales.
Precision improvement of a platform scale cannot be achieved by simply employing a higher precision weighing type. It is also necessary to assure mechanical strength to tolerate a heavy object. There is a need for providing a construction capable of stably weighing heavy objects.
Particularly, in case of weighing a heavy object, there arises a problem of bending a support member for supporting the object to be weighed due to the weight thereof.
As shown in FIG. 10 (a), in case of placing a heavy object 600 on a flat weighing dish 500, it may bend as shown in FIG. 10 (b). As a result, stress may develop in the horizontal direction with respect to the load detection section 400 that supports the weighing dish 500. Such force in the horizontal direction causes an error in the load detection section 400 that detects the load in the vertical direction, thereby degrading detection precision.
As shown in FIG. 11, in order to reduce such error, any conventional weighing machines for weighing heavy objects interpose a component force damping device 304 (see FIG. 11 (b)) between a support member 305 that supports an object to be weighed and a load detection section 303 by sandwiching a ball 311 with a pair of bearing plates 312 and 313 (see FIG. 11 (a)).
In this particular configuration, any horizontal stress due to bend of the support member 305 is released by the component force damping device 304, thereby keeping the load detection section 303 unaffected.